6.2L start then stumble and die

[wjonesgt]

So picked up my 2012 6.2L with 96k miles in Dec 2017. It’s always had a little bit of a shake at idle, not terrible,  but noticeable.  But no other issues until now.

Recently, last month or so, I started having an issue at first start up in the mornings. The truck will fire quickly, idle up as it should, but then stumble a little for about 3 seconds, then smooth out and idle and start fine the rest of the day. It started as just a noticeable stumble, but has turned into a stalling condition. Now, I will start the truck, it will idle up, then stumble and die. Restart the truck and it will start fine. Does have a stronger shaking feel, like a random miss for a few seconds, but will smooth out and be normal.

I can feather the gas while it is stumbling and keep it from dying. 

 

Here is what all I have done so far:

replaced plugs and wires with OE spec parts

Cleaned then replaced MAF

replaced cam pos sensor

replaced throttle pos sensor

replaced coolant temp sensor

cleaned throttle body

seafoam spray thru the throttle body

2 cans of seafoam in one take of gas

cleaned MAP sensor

sprayed all over checking for vacuum leaks

fuel pressure at the rail is 60psi, settles down to about 55psi while running

 

no codes

 

i do have a predator 2 arriving tommorow, so I can play with some settings. 

 

Anyone have ave any other ideas, while I continue to beat my head against the wall?

 

thanks. 

 

[Supreme Pizza]

How much do you have into this so far? I would guess several hundred. I would not change any settings with your "predator 2", until you have resolved the issue. 

 

Many times people have one issue, but they spend hundreds of dollars and just wind up complicating the issue. Lets say you have a faulty sensor. You replace 10 other things, and during this process, you mess up a few other things. Now you have turned one problem into 3 problems. It is a very expensive way to make the problem worse. 

 

Sometimes ya just have to hire a good diagnostic guy to solve the problem. I HATE hiring diagnostic guys, but sometimes its the best option. 

 

I guess it would be like replacing random human organs to see which one solves what ever health problem is happening. It only makes things worse, wont solve the issue, and is very expensive. 

[swathdiver]

It is near impossible to properly diagnose these trucks without a Tech2 or modern scan tool.  Something is weak but not quite out of spec if there are no codes.  I would be looking at Fuel Trims (for vacuum leaks), fuel line pressure bleeding down, and even triple checking your new parts.  Do you happen to live in the Sunshine State?  

[wjonesgt]

I did check fuel trims. LTFT is at 6%, so I don’t think there is an issue there. Line pressure holds steady for several minutes after shutting down the truck. I know it bleeds off overnight, but I didn’t watch the gage past a couple minutes. 

A friend of mine recently mentioned trying a TPS relearn. He says he’s seen those drive by wire throttle bodies do crazy things when opened up. I’m going to try that today. 

[dsmmace]

Motor mount condition is ok? If so I would reset the fuel trims and do an idle relearn to start.